Up to now, an alnico magnet, a ferritic magnet, a Sm—Co magnet, an Nd—Fe—B magnet ant the like are well known as a permanent magnet. The suitable magnets are respectively used as key parts in various motors such as VCM and spindle motor; and other various electric equipments such as measuring equipment, loudspeaker and MRI for medical treatment according to their specifications. Among these magnets, the rare earth based magnet such as the Sm—Co magnet, Nd—Fe—B magnet and the like contain rare earth element(s) and a high amount of Fe or Co. Fe and Co contribute to the increase of saturation flux density (Br). And the rare earth elements contribute to the increase of coercivity (HcJ) and thus good magnetic properties can be realized because the rare earth elements bring out a greatly high magnetic anisotropy which is derived from the movement of 4f electron in the crystal field.
Recently, demands for miniaturization and energy saving of various electric equipments are increasing, and higher maximum energy product [(BH)max] and higher coercivity are required compared to the permanent magnet used as the materials for key parts of these equipments. Therefore, the rare earth based magnet with high performance, especially R-T-B based magnet is widely used in various fields. And, many studies are carried out to get higher coercivity.
As for the techniques to improve the coercivity of the R-T-B based magnet, for example, these is a technique in which heavy rare earth elements such as Dy or Tb are added. A method has been provided in which Dy is deposited at the outside of the sintered body and then Dy is diffused to the internal grain boundary (Patent Document 1). Besides, a method in which fluoride of Dy and the like is coated to the surface of the sintered body has been proposed (Patent Document 2).